Molded plastic articles are becoming widely accepted as a replacement for metallic and glass articles. One advantage associated with molded plastic articles is the integration of several components into one article, thereby reducing the number of assembly operations. In other words, an article that previously was comprised of several components bonded or joined together may be manufactured in a one step, molding operation. One inherent problem that has resulted from the advent of this practice is the ability to print upon the resulting complex (concave, convex, etc.) surface shape of the article. Printing is desirable since other means for disposing images are timely and the use of several 2-dimensional printing concepts, namely screen-printing and pad-printing, have been extended to meet this need with only limited success.
Screen-printing is a known commercial process and is described in greater detail below. Screen printing is limited in the complexity of the surface upon which may be printed. This technique represents a very economical method for printing onto a “flat” substrate. Screen-printing has been applied to curved surfaces through the implementation of a technique known as in-mold decoration (IMD). In this technique the printed image is applied via screen-printing to a “flat” film. This film is then held via vacuum to the surface of the mold. The film becomes part of the surface of the article upon the injection of the plastic material into the mold. Major difficulties associated with the use of this technique are the registration of the decoration on the article's surface and a limitation in surface complexity of the article. Decoration registration requires accurate positioning of the film into the mold for each article reproduction. Surface complexity is limited by the ability of the film to conform (e.g., stretch) to the shape of mold to be incorporated as part of the article's surface.
Pad-printing is also a known commercial printing process and is described in greater detail below. Pad-printing is a printing process which uses a tampon and a cliché to stamp or print onto a convex curved surface. In fact, pad-printing or tampography is a form of indirect or offset gravure printing that is accepted by the automotive industry for the decoration of interior components. Pad or tampon printing is an economical technique capable of providing fine line (32 micrometer) resolution on both curved and uneven surfaces. However, this technique is limited in the degree of complex curvature, radius, and size of the substrate to be printed, as well as in the design of the substrate's edge up to which one may desire to print.
Membrane image transfer (MIT) printing (discussed below) is a new printing concept that combines both screen-printing and pad printing (tampography) into one method for the decoration of articles with complex shape. MIT printing offers the ability to print articles with complex shape with the print resolution and opacity normally obtained with screen-printing on flat substrates. However, manufacturers have been challenged in optimizing variables related to the performance of ink in MIT printing and improving this process related to screen printing of an image onto a membrane and transferring the image from the membrane to a substrate.